Renal Control of Body Fluid Volume and Circulatory Dynamics

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A major theme of this Program Project has been the renal-body fluid feedback control system in which the kidneys play a dominant role in the long-term regulation of body fluid volumes and arterial pressure. A common renal abnormality that has been found in all forms of hypertension examined to date, including genetic and experimental models and human essential hypertension is a hypertensive shift in the pressure natriuresis relationship. A major objective of Project II "is to examine the interactions between endothelin, nitric oxide, oxidative stress and novel anti-angiogenic factors in mediating the reduction in renal-pressure natriuresis in a specific form of hypertension associated with endothelial dysfunctionpreeclampsia (PE). Hypertension associated with PE develops during pregnancy and remits after parturition implicating the placenta as a central culprit in the disease. The initiating event in PE is postulated to involve reduced placental perfusion that leads to widespread maternal vascular endothelial dysfunction by mechanisms that remain to be elucidated. Recent studies in preeclamptic women have demonstrated increased placental and circulating concentrations of soluble fms-like tyrosine kinase-1 (sFlt-1), a naturally occurring antagonist of vascular endothelial growth factor (VEGF) and placental growth factor (PIGF). Increased sFlt-1 during preeclampsia is associated with decreased free plasma VEGF and PIGF. Moreover, adenovirus mediated administration of sFlt-1 to pregnant rats to mimic plasma concentrations observed in preeclamptic women, decreases free VEGF and PIGF and produces hypertension and proteinuria. Although these novel findings implicate sFlt-1 in the pathogenesis of hypertension during preeclampsia, what remains unclear are the specific mechanisms that lead to excess sFlt- 1 production and the mechanisms whereby sFlt-1 increases blood pressure during pregnancy. Based on our preliminary data, we propose to test the central hypothesis that reduced uterine perfusion pressure (RUPP) in the pregnant rat increases placental sFlt-1 via ANGII and TNF-ct dependent mechanisms. The increase in plasma concentration of sFlt-1, in turn results in decreased plasma concentrations of VEGF and PIGF. In addition, we propose that chronic sFlt-1 excess during pregnancy impairs renal function and increases total peripheral resistance and blood pressure by decreasing plasma concentrations of free VEGF and PIGF which contribute to endothelial cell dysfunction marked by enhanced production of ET-1, ROS and decreased NO. To test this hypothesis arterial pressure, renal, hormonal, and endothelial factors will be examined in a conscious, chronically instrumented rat model of PE produced by long-term RUPP. In addition to the RUPP model, a sFlt-1 model of PE will be used to determine the interaction between sFlt-1 and ET-1, ROS, and NO production while an in vitro placental explant model will be used to examine the direct interaction between hypoxia and placental sFlt-1, ANGII, and TNF-a production.